“Slide-ring gels”, new gels different from physical gels and chemical gels, have been developed in recent years. A compound that is used for such slide-ring gels and is drawing attention is a crosslinked polyrotaxane.
A crosslinked polyrotaxane has a structure in which linear molecules thread through cyclic molecules in a skewered manner and the cyclic molecules are movable along the linear molecules (has a pulley effect). The pulley effect allows the crosslinked polyrotaxane to be viscoelastic and to uniformly distribute tensile force applied thereto. The crosslinked polyrotaxane is therefore not likely to have cracks or flaws, i.e., has excellent characteristics that conventional crosslinked polymers do not have. Such a crosslinked polyrotaxane is obtainable by placing a capping group at each end of a linear molecule of pseudopolyrotaxanes to prevent dissociation of the cyclic molecules of pseudopolyrotaxanes and crosslinking the resulting polyrotaxanes. The pseudopolyrotaxanes have a linear molecule which is included in the cavities of the cyclic molecules in a skewered manner.
Patent Literature 1 describes a method for obtaining a polyrotaxane which includes mixing a carboxylated polyethylene glycol and a cyclodextrin to obtain a pseudopolyrotaxane that has a carboxylated polyethylene glycol molecule which is included in the cavities of the cyclodextrin molecules in a skewered manner, and capping each end of the pseudopolyrotaxane.